Computer-implemented process and computer system for raster displaying video data using foreground and background commands

ABSTRACT

Video data for two or more video streams are processed by a single background command list containing one or more background commands and a single foreground command list containing one or more foreground commands, where the foreground command list is implemented only during a vertical blanking interval of the display raster of a monitor. The processed video data are then displayed during the raster period. In a preferred embodiment, if the implementation of a background command has not completed by the start of a vertical blanking interval, the background command is interrupted, the state of the background command implementation is saved, the foreground command list is implemented, and then the interrupted background command is resumed. The background commands are preferably those that do not directly affect the display bitmaps, while the foreground commands are those that do directly affect the display bitmaps. The invention assures proper synchronization of video data processing and raster-based video display.

This is a continuation of Ser. No. 08/152,347 filed on Nov. 12, 1993 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to video processing, and, in particular, to computer-implemented processes and computer systems for processing video data for display on a raster-based monitor.

2. Description of the Related Art

Personal computer (PC) systems for capturing and compressing video signals and for decompressing and displaying compressed video signals on a computer monitor are known. Some such PC systems have a general-purpose host processor and a special-purpose video hardware subsystem. These PC systems may also have an application program, a general-purpose video software program, and a special-purpose video driver running on the host processor, and special-purpose video-processing microcode running on the special-purpose video hardware subsystem.

To process video data, the application program interfaces with the general-purpose video software program. The video software program in turn interfaces with the special-purpose video driver. The video driver also interfaces with the special-purpose video-processing microcode which runs on the video hardware subsystem.

For example, the host processor may be an Intel® 486 microprocessor, the video hardware subsystem may be an Intel® Smart Video Recorder card or other hardware based on an Intel® i750® Pixel Processor, and the video software program may be a version of Microsoft® Video for Windows. The video driver and the video-processing microcode may be delivered with the video hardware subsystem. The video-processing microcode that is provided with the video hardware subsystem performs compression and decompression of video data using specific video algorithms.

It is desirable for users of video hardware subsystems to be able to run microcode on those subsystems other than the video-processing microcode provided with the subsystems. For example, a user may wish to implement video compression and/or decompression algorithms different from those supported by the provided video-processing microcode. In addition or alternatively, a user may wish to perform data processing other than that supported by the provided video-processing microcode. This data processing need not even be related to the processing of video data.

Under the known PC systems described above, it is difficult for a user to process data on a video hardware subsystem other than by the algorithms supported by the video-processing microcode provided with the subsystem. For example, it currently is difficult for a user to program a pixel processor such as an Intel® i750® Pixel Processor to implement algorithms other than those supported by the video-processing algorithms provided with the pixel processor.

Furthermore, the special-purpose video hardware subsystems and special-purpose video drivers of the known PC systems constitute closed architectures. That is, the video driver is designed specifically for the particular video hardware subsystem and is not easily modified to support alternative hardware configurations. As a result, each generation of improved and upgraded hardware subsystem requires extensive modification to the video driver.

It is accordingly an object of this invention to overcome the disadvantages and drawbacks of the known art and to provide a video driver that permits a user to program easily a video hardware subsystem of a PC system.

It is a particular object of the present invention to provide a video driver that permits a user to program easily a pixel processor such as a version of the Intel® i750® Pixel Processor.

It is a further object of the present invention to provide a video driver that provides an interface between the video hardware subsystem of a PC system and a video software program running on a host processor, where the video driver permits a user to implement compression and/or decompression algorithms different from those already supported by the video driver and video-processing microcode that are provided with the video hardware subsystem.

It is a particular object of the present invention to provide a video driver that provides an interface between a pixel processor such as a version of the Intel® i750® Pixel Processor and a version of Microsoft® Video for Windows running on a host processor such as an Intel® 486 processor, where the video driver permits a user to implement compression and/or decompression algorithms different from those already supported by the video-processing microcode that is provided with the pixel processor.

It is a further object of the present invention to provide a video driver that may be easily modified to support alternative video hardware subsystem configurations.

It is a particular object of the present invention to provide a video driver that is easily modified to support improved and upgraded versions of pixel processors.

It is a further object of the present invention to provide computer-implemented processes and computer systems based on the video drivers described above.

It is a further object of the present invention to provide computer-implemented processes, video hardware subsystems, and computer systems for displaying full-screen video images on computer monitors without having to create scaled bitmaps.

It is a further object of the present invention to provide computer-implemented processes and computer systems for processing video data for display on raster-based monitors.

Further objects and advantages of this invention will become apparent from the detailed description of a preferred embodiment which follows.

SUMMARY OF THE INVENTION

The present invention is a computer-implemented process and a computer system for raster displaying two or more streams of video data on a monitor. The video data are processed by implementing a single background command list comprising one or more background commands. The video data are also processed by implementing a single foreground command list comprising one or more foreground commands, where the foreground command list is implemented only during a vertical blanking interval of the display raster of the monitor. The processed video data is then displayed.

In an alternative preferred embodiment of the present invention, a display bitmap corresponding to the video data is raster displayed. During the raster display of the display-bitmap, the video data are processed by implementing a single background command list comprising one or more background commands, wherein the implementation of the background command list does not alter the display bitmap. The video data are then processed by implementing a single foreground command list comprising one or more foreground commands, wherein the foreground command list is only implemented during a vertical blanking interval of the display raster of the monitor, wherein the implementation of the foreground command list alters the display bitmap. The altered display bitmap is then raster displayed after the vertical blanking interval.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiment, the appended claims, and the accompanying drawings in which:

FIG. 1 is a block diagram of the hardware architecture of a video system according to a preferred embodiment of the present invention;

FIG. 2 is a block diagram of the software architecture of the video system of FIG. 1;

FIG. 3 is a process flow diagram of the decompression and display processing implemented by the video system of FIGS. 1 and 2;

FIG. 4 is a process flow diagram of the capture and compression processing implemented by the video system of FIGS. 1 and 2;

FIG. 5 is a process flow diagram of the monitoring of capture/compression processing implemented by the video system of FIGS. 1 and 2;

FIG. 6 is a representation of the video driver of FIG. 2;

FIG. 7 is a process flow diagram of the processing implemented by the video system of FIGS. 1 and 2 to display full-screen video images; and

FIG. 8 is a process flow diagram of the processing of the run process manager of the video driver of FIG. 2 to coordinate the implementation of commands contained in the background and foreground command lists.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention is directed to a video driver for a video hardware subsystem, such as a video-processing card with a version of the Intel® i750® Pixel Processor, where the video driver permits a user to program the video hardware subsystem easily. In a preferred configuration, the video driver provides an interface between a general-purpose video software program running on a general-purpose host processor (e.g., a version of Microsoft® Video for Windows software running on an Intel® 486 microprocessor) and a video hardware subsystem. In this configuration, the user may choose to compress and/or decompress video clam using algorithms provided with the video hardware subsystem or using alternative algorithms provided by the user. The user may also use the video driver to program the video hardware subsystem to implement functions other than video compression and decompression.

Referring now to FIG. 1, there is shown a block diagram of the hardware architecture of video system 100, according to a preferred embodiment of the present invention. Video system 100 comprises video hardware subsystem 104, video camera 102, graphics generator 106, monitor 108, host processor and memory 110, mass storage device 112, and bus 114. Video hardware subsystem 104 comprises capture hardware module 116, programmable processor 118, VRAM memory device 120, display hardware module 122, and bus interface 124.

Video system 100 may be used to decompress video dam stored in mass storage device 112 for display on monitor 108. Video system 100 may also be used to capture and compress video signals generated by camera 102. In addition, video system 100 is capable of displaying video images on monitor 108 during capture and compression processing. The displayed video images during capture and compression processing may be either the raw captured video images or the companded images generated during video compression (i.e., the results of decompressing the compressed video data).

Referring now to FIG. 2, there is shown a block diagram of the software architecture of video system 100 of FIG. 1, according to a preferred embodiment of the present invention. Application program 202, general-purpose video software program 204, and video driver 206 run on host processor 110 of FIG. 1. Microcode 208 runs on the processors and modules of video hardware subsystem 104 of FIG. 1.

Video Processing

Referring now to FIG. 3, there is shown a process flow diagram of the decompression and display processing implemented by video system 100 of FIGS. 1 and 2, according to a preferred embodiment of the present invention. In decompression and display processing, video software program 204 reads compressed video buffer data from mass storage device 112 via bus 114 and passes the buffer data to video driver 206 (block 302 of FIG. 3). Video driver 206 passes compressed video bitstream data to bus interface 124 via bus 114 (block 304). Bus interface 124 stores the compressed video bitstream data to VRAM 120 (block 306).

Programmable processor 118 reads the compressed video bitstream data from VRAM 120, decompresses the video data using microcode 208, and stores decompressed video bitmaps back to VRAM 120 (block 308). The microcode used by programmable processor 118 to decompress the video data is selected by the host processor. The selection is based on the information stored in the compressed bitstream header and a list of available algorithms listed in a configuration file. The user may choose to use the video decompression algorithms provided with the video driver 206 or implement alternative video decompression algorithms that are compatible with video driver 206. The microcode used to implement these alternative decompression algorithms may be developed by the user or other third parties.

Programmable processor 118 reads the decompressed video bitmaps from VRAM 120, scales the video data for display, and stores scaled video bitmaps back to VRAM 120 (block 310). Display hardware module 122 reads the scaled video bitmaps from VRAM 120, optionally merges the video data with graphics data received from graphics generator 106, converts the digital video/graphics data to analog video/graphics signals, and transmits the analog video/graphics signals to monitor 108 (block 312). Monitor 108 displays the analog video/graphics signals (block 314).

Referring now to FIG. 4, there is shown a process flow diagram of the capture and compression processing implemented by video system 100 of FIGS. 1 and 2, according to a preferred embodiment of the present invention. In capture and compression processing, camera 102 of video system 100 generates and transmits analog video signals to capture hardware module 116 (block 402 of FIG. 4). Capture hardware module 116 digitizes the analog video signals and stores uncompressed "full frame" video bitmaps to video random access memory (VRAM) device 120 (block 404). In a preferred embodiment, capture hardware module 116 captures video data as subsampled YUV 4:1:1 bitmaps (i.e., 9 bits per pixel). In alternative preferred embodiments, other video data formats may be used.

Programmable processor 118 reads the uncompressed video bitmaps from VRAM 120, compresses the video data using microcode 208, and stores compressed video bitstream data and companded video bitmaps back to VRAM 120 (block 406). The user selects the microcode used by programmable processor 118 to compress the video data. The user may choose to use the video compression algorithms provided with video driver 206 or user implemented alternative video compression algorithms that are compatible with video driver 206. The microcode used to implement these alternative compression algorithms may be developed by the user or other third parties.

Bus interface 124 copies the compressed video bitstream data to host memory 110 via bus 114 (block 408). Video driver 206 passes the video buffer data to general-purpose video software program 204 (block 410). Video software program 204 writes the compressed video buffer data to mass storage device 112 via bus 114 (block 412).

Referring now to FIG. 5, there is shown a process flow diagram of the monitoring of capture/compression processing implemented by video system 100 of FIGS. 1 and 2, according to a preferred embodiment of the present invention. In capture/compression monitoring, programmable processor 118 reads either the uncompressed "full frame" video bitmaps or the companded video bitmaps from VRAM 120, scales the video data for display, and stores scaled video bitmaps back to VRAM 120 (block 502 of FIG. 5). If the uncompressed "full frame" video bitmaps are selected, the capture/compression monitoring monitors the video data as it is captured. If the companded bitmaps are selected, then capture/compression monitoring monitors the video data after the image has been compressed and decompressed ("companded").

Display hardware module 122 reads the scaled video bitmaps from VRAM 120, optionally merges the video data with graphics data received from graphics generator 106, converts the video/graphics data to analog video/graphics signals, and transmits the analog video/graphics signals to monitor 108 (block 504). Monitor 108 displays the analog video/graphics signals (block 506).

Referring again to FIG. 1, camera 102 may be any suitable video camera that generates analog video signals supported by video system 100. In other preferred embodiments, the analog video signals may be generated by an alternative local source such as a VCR or laserdisc. Capture hardware module 116 may be any suitable module for digitizing analog video signals and capturing digital video bitmaps and is preferably an Intel® ActionMedia® II Capture Module.

Memory 120 may be any suitable computer memory device for storing data during video processing such as a random access memory (RAM) device and is preferably a video RAM (VRAM) device with at least 2 megabytes of data storage capacity. Programmable processor 118 may be any suitable processor for compressing and decompressing video data and is preferably a version of the Intel® i750® Pixel Processor. Bus interface 124 may be any suitable hardware for transmitting data from VRAM 120 to bus 114 and for receiving data from bus 114 for storage to VRAM 120. Bus 114 may be any bus suitable for communicating data and is preferably an Industry Standard Architecture (ISA) PC bus.

Display hardware module 122 may be any suitable module for processing and merging scaled video bitmap data with graphics data for display on a suitable monitor and is preferably a version of the Intel® i750® Display Processor. Graphics generator 106 may be any suitable source of graphics data and preferably generates VGA graphics data. In an alternative preferred embodiment, graphics generator 106 is optional and may be remove entirely. In another alternative preferred embodiment, the functions of graphics generator 106 may be implemented by display hardware module 122, in which case graphics generator 106 may be considered part of video hardware subsystem 104. Monitor 108 may be any suitable device for displaying analog video/graphics data and is preferably a VGA monitor.

Host processor 110 may be any suitable general-purpose processor and is preferably an Intel® 486 microprocessor. Those skilled in the art will understand that alternative preferred embodiments of the present invention may use another Intel® processor such as an Intel® 386 or Pentium microprocessor. Host processor 110 preferably has at least 4 megabytes of host memory.

Mass storage device 112 may be any suitable device for storing compressed video data and is preferably a hard disk drive having at least 100 megabytes of data storage capacity. Those skilled in the art will understand that, in alternative preferred embodiments, the source of compressed video data may be a CD-ROM player. It will also be understood that alternative preferred embodiments of the video system of the present invention may be used to transmit and receive compressed video data to and from one or more remote locations. As such, the video system of the present invention may be one node of a local or wide area network communicating via various media such as an Ethernet bus or T1 lines. Under such configurations, the video system of the present invention may support various video functions such as teleconferencing, broadcasting, and multicasting.

Referring again to FIG. 2, application program 202 may be any suitable application-level software that requires video processing. General-purpose video software program 204 may be any suitable program for interfacing between application program 202 and video driver 206 and is preferably a version of Microsoft® Video for Windows software program. Alternatively, general-purpose video software program 204 may be Apple QuickTime® for Windows. As described earlier, microcode 208 may comprise the video compression/decompression software provided with video hardware subsystem 104. Alternatively, microcode 208 may be video compression and/or decompression software provided by the user or other third party.

Video Driver

Referring now to FIG. 6, there is shown a representation of video driver 206 of FIG. 2, according to a preferred embodiment of the present invention. Video driver 206 comprises a number of software modules that reside on host processor 110 of FIG. 1. These software modules provide the interfaces with general-purpose video software program 204 running on host processor 110 and microcode 208 running on video subsystem 104. In the preferred embodiment of FIGS. 1 and 2, general-purpose video software program 204 is a version of Microsoft® Video for Windows software program (VfW).

Video driver 206 provides or supports the following capabilities:

Receipt and handling of messages to and from VfW for video data processing (message handler 602).

Selection and loading of microcode onto video hardware subsystem 104 for implementing video processing within the VfW environment (algorithm manager 604).

Allocation of memory space within VRAM 120 (memory manager 606).

Implementation of copy/scale function by video hardware subsystem 104 (copy/scale manager 616).

Implementation of full-screen display of video images by video hardware subsystem 104 (view manager 608).

Implementation of video window clipping (clipping manager 614).

Capturing of analog video signals by video hardware subsystem 104 (capture manager 618).

Managing of interrupt service routines (interrupt service routine manager 620).

Managing "plug & play" capabilities of video hardware subsystem (plug & play manager 622).

Implementation of background and foreground commands on video hardware subsystem 104 (run process manager 624).

Loading and converting of object files (COFF file parser 612).

Selection, loading, and running of microcode on video hardware subsystem 104 outside of the VfW environment (microcode manager 610).

These capabilities are described in greater detail in the following sections of the specification.

Handling Microsoft® Video for Windows Messages

Message handler 602 of video driver 206 handles the messages required to interface with Microsoft® Video for Windows. These messages include:

Draw stream messages for displaying video data on monitor 108.

Decompression stream messages for decompressing a stream of compressed video data.

Compression stream messages for compressing a stream of uncompressed video dam.

Capture stream messages for capturing analog video signals as digital video data.

General messages handled by all Microsoft® Windows device drivers, including Open/Close/Load/Free etc. Those skilled in the art will understand that these messages are required for any Microsoft® Windows 3.1 device driver.

Those skilled in the art will understand that message handler 602 is designed to meet the requirements of Microsoft® Video for Windows.

Selection and Loading of Video-Processing Microcode

Algorithm manager 604 handles the selection and loading of video algorithm microcode 630 for implementing video compression and/or decompression algorithms on programmable processor 118 within the Microsoft® Video for Windows environment. As such, algorithm manager 604 provides the interface between video driver 206 and external libraries for implementing compression/decompression algorithms. In a preferred embodiment, the external libraries are dynamically linked libraries (DLLs) under the Microsoft® Windows graphical user interface. In alternative preferred embodiments, the external libraries may operate under DOS, OS/2, MAC, and UNIX operating systems. As described earlier, a user of video system 100 may process video data using the compression/decompression algorithms supported by the microcode provided with video hardware subsystem 104. Alternatively, the user may process video data using video-processing microcode not provided with video hardware subsystem 104. This microcode may implement video compression and/or decompression algorithms different from the microcode provided with video hardware subsystem 104.

A DLL containing video algorithm microcode 630 is installed for use by video driver 206 by inserting specific information in the [drivers] and [Indeo₋₋ Algs] sections of the SYSTEM.INI file of Microsoft® VfW. Specifically, the [drivers] section is updated by adding a configuration line of the following format:

    VIDC.4 cc=draw1.drv

where 4 cc is the four-character code assigned to the algorithm to be loaded. The [drivers] section may have one or more of these configuration lines, each with a different four-character code.

The user-defined [Indeo₋₋ Algs] section is created or updated by adding a configuration line of the following format:

    4 cc=DLLname.dll, Long name of alg, flags

where flags indicates the type of algorithm (i.e., E for encode, D for decode, and B for both encode and decode). DLLname may include path, but is limited to 128 characters. Long name of alg may be up to 30 characters in length.

For video compression, Microsoft® VfW tells video driver 206 to select the video compression algorithm to run. Video driver 206 responds by returning the header that identifies which compression algorithm is being used. For video decompression, Microsoft® VfW examines the header of the compressed bitstream to determine the video decompression algorithm to be used. Microsoft® VfW then sends video driver 206 a message identifying the appropriate decompression algorithm to be used.

To be successfully loaded and used by video driver 206, the algorithm DLL is preferably designed with the following constraints:

The algorithm DLL is designed for Microsoft® Windows version 3.1 or later.

The algorithm DLL is coded to the Loadable Algorithm Interface specification.

Video driver 206 communicates with the loaded algorithm DLL by making calls to a message function called alg₋₋ proc0 within the DLL and passing messages to it. The alg₋₋ proc0 function is written to match the following calling parameters delivered by video driver 206:

dwAlgInstId--A DWORD variable that identifies the algorithm instance.

uiAlgMsg--A UINT variable that forms the message to the algorithm DLL.

lparam1--A generic long variable used to pass values of unknown type.

lparam2--A generic long variable used to pass values of unknown type.

The following are the messages delivered to alg₋₋ proc0 and the definition of associated parameters passed.

ALG OPEN

Video driver 206 sends an ALG₋₋ OPEN message to instruct the algorithm DLL to allocate any instance data required for processing and return a handle unique to that instance. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ OPEN are:

dwAlgInstId--Undefined

uiAlgMsg--ALG₋₋ OPEN

lparam1--Far pointer to a DWORD to be filled in with a unique instance handle for this opening of the algorithm DLL. This handle ID will be passed back to the algorithm DLL during subsequent calls to alg₋₋ proc0.

lparam2--Far pointer to a LITEFUNCS structure containing far pointers to video driver functions needed by the algorithm DLL.

The LITEFUNCS structure contains far pointers to the following video driver functions:

*pfLoadUcode (Filename, VramPtr, hModule)--Loads microcode from disk into VRAM.

*pfUnLoadUcode (Filename, VramPtr)--Unloads microcode from VRAM.

*pfHost2Vram (HostPtr, HostOff, VramPtr, Len)--Transfers data from the host to VRAM.

*pfVram2Host (VramPtr, HostPtr, HostOff, Len)--Transfers data from VRAM to the host.

*pfAm2ReadShort (VramPtr)--Reads a SHORT value from VRAM and returns it.

*pfAm2ReadLong (VramPtr)--Reads a LONG value from VRAM and returns it.

*pfAllocVMem (Size, Align)--Allocates a VRAM buffer. Returns VRAM pointer.

*pfFreeVMem (VramPtr)--Frees a VRAM buffer.

*pfResource2Vram (Resource, VramPtr, hModule)--Loads a resource file into VRAM.

In these video driver functions,

Filename=name of microcode file.

VramPtr=pointer to location in VRAM.

hModule=Microsoft® Windows handle to a module containing a desired resource.

HostPtr=pointer to location in host memory.

HostOff=offset from host memory location.

Len=length of data to be transferred.

Size=size of buffer to be allocated.

Align=Boundary on which code/data must start (e.g., segment, paragraph, word).

Resource=name of resource file.

ALG₋₋ CLOSE

Video driver 206 sends an ALG₋₋ CLOSE message to instruct the algorithm DLL to free any instance data associated with this instance. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ CLOSE are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ CLOSE.

lparam1--Undefined.

lparam2--Undefined.

ALG₋₋ LOAD₋₋ PLAYBACK

Video driver 206 sends an ALG₋₋ LOAD₋₋ PLAYBACK message to instruct the algorithm DLL to load all resources and microcode associated with playback. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ LOAD₋₋ PLAYBACK are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ LOAD₋₋ PLAYBACK.

lparam1--Far pointer to a STREAMALGINFO structure.

lparam2--Far pointer to a BITMAPINFOHEADER structure of Microsoft® VfW.

The STREAMALGINFO structure contains the following parameters:

AlgInst--Algorithm open instance handle.

AlgEntryPoint--VRAM address of the algorithm DLL entry point.

*pCodecArgs--Far pointer to CODEC₋₋ ARGS structure.

CodecArgsSize--Size of CODEC₋₋ ARCS structure plus extra algorithm DLL space.

The CODEC₋₋ ARGS structure contains the following parameters:

CODEC₋₋ ARGS₋₋ HDR Hdr--Common CODEC₋₋ ARGS header (filled in by video driver 206).

VWORD AlgSpecific[0]--Algorithm-specific codec arguments of variable length.

The CODEC₋₋ ARGS₋₋ HDR structure contains the following parameters:

PrevBitmap[3]--VRAM addresses of previous Y, V, and U bitmaps, respectively.

CurBitmap[3]--VRAM addresses of current Y, V, and U bitmaps, respectively.

Pitch[3]--Pitches of Y, V, and U bitmaps, respectively.

CompressedBuf--VRAM address of the compressed data buffer.

Those skilled in the art will understand that video driver 206 supports color formats other than YUV, such as RGB, YIQ, and HSV.

ALG₋₋ UNLOAD₋₋ PLAYBACK

Video driver 206 sends an ALG₋₋ UNLOAD₋₋ PLAYBACK message to instruct the algorithm DLL to free the playback microcode and any resources used for this instance. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ UNLOAD₋₋ PLAYBACK are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ UNLOAD₋₋ PLAYBACK.

lparam1--Undefined.

lparam2--Undefined.

ALG₋₋ LOAD₋₋ CAPTURE

Video driver 206 sends an ALG₋₋ LOAD₋₋ CAPTURE message to instruct the algorithm DLL to load all resources and microcode associated with capture. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ LOAD₋₋ CAPTURE are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ LOAD₋₋ CAPTURE.

lparam1--Far pointer to a STREAMALGINFO structure.

lparam2--Far pointer to a BITMAPINFOHEADER structure of Microsoft® VfW.

ALG₋₋ UNLOAD₋₋ CAPTURE

Video driver 206 sends an ALG₋₋ UNLOAD₋₋ CAPTURE message to instruct the algorithm DLL to free the capture microcode and any resources used for this instance. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ UNLOAD₋₋ CAPTURE are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ UNLOAD₋₋ CAPTURE.

lparam1--Undefined.

lparam2--Undefined.

ALG₋₋ GETINFO

Video driver 206 sends an ALG₋₋ GETINFO message to instruct the algorithm DLL to provide information describing the algorithm DLL. The algorithm DLL fills in the ICINFO structure passed. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ GETINFO are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ GETINFO.

lparam1--A far pointer to the ICINFO structure of Microsoft® VfW.

lparam2--Undefined.

ALG₋₋ DECOMPRESS₋₋ QUERY

Video driver 206 sends an ALG₋₋ DECOMPRESS₋₋ QUERY message to query the algorithm DLL to determine if the algorithm DLL can decompress a specific input format, or if the algorithm DLL can decompress the input format to a specific output format. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ DECOMPRESS₋₋ QUERY are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ DECOMPRESS₋₋ QUERY.

lparam1--Far pointer to the Microsoft® VfW BITMAPINFOHEADER of the input bitmap.

lparam2--Far pointer to the Microsoft® VfW BITMAPINFOHEADER of the output bitmap.

ALG₋₋ DECOMPRESS₋₋ GET₋₋ FORMAT

To playback a video image, video driver 206 sends an ALG₋₋ DECOMPRESS₋₋ GET₋₋ FORMAT message to query the algorithm DLL to determine the format of the decompressed dam. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ DECOMPRESS₋₋ GET₋₋ FORMAT are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ DECOMPRESS₋₋ GET₋₋ FORMAT.

lparam1--Far pointer to a INOUTBIH structure.

lparam2--Far pointer to a DWORD to be filled in with the decompressed bitmap size.

The INOUTBIH structure contains the following parameters:

BITMAPINFO FAR*pIn--Far pointer to a Microsoft® VfW BITMAPINFO structure.

BITMAPINFO FAR * pOut--Far pointer to another Microsoft® VfW BITMAPINFO structure.

ALG₋₋ GET₋₋ ENCODE₋₋ FORMAT

Video driver 206 sends an ALG₋₋ GET₋₋ ENCODE₋₋ FORMAT message to inform the algorithm DLL of the format to be used by the algorithm DLL to compress the input video. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ GET₋₋ ENCODE₋₋ FORMAT are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ GET₋₋ ENCODE₋₋ FORMAT.

lparam1--Far Pointer to the Microsoft® VfW BITMAPINFOHEADER structure.

lparam2--Undefined.

ALG₋₋ VIDEO₋₋ FORMAT₋₋ DIALOG

The user has the option of setting various capture parameters, such a contrast, tint and brightness, from a dialog box. Video driver 206 provides this information to the algorithm DLL by the ALG₋₋ VIDEO₋₋ FORMAT₋₋ DIALOG message. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ VIDEO₋₋ FORMAT₋₋ DIALOG are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ VIDEO₋₋₋ FORMAT₋₋ DIALOG.

lparam1--Handle to the video effects dialog box.

lparam2--Undefined.

ALG₋₋ PREDECODE

Before the decode of each frame, video driver 206 sends an ALG₋₋ PREDECODE message to instruct the algorithm DLL to copy the compressed data from the VfW host buffer into VRAM using the *pfHost2Vram function. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ PREDECODE are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ PREDECODE.

lparam1--Far pointer to PREDECODE₋₋ PARMS structure.

lparam2--Undefined.

The PREDECODE₋₋ PARMS structure contains the following parameters:

CODEC₋₋ ARGS FAR *pCA--Pointer to parameters needed by decode microcode.

WORD CodecArgsSize--Size of parameters needed by decode microcode.

void HUGE *pFrameData--Pointer to compressed frame data.

DWORD FrameDataSize--Size of compressed frame data

ALG₋₋ PREENCODE

Video driver 206 sends an ALG₋₋ PREENCODE message before the encode of each frame. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ PREENCODE are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ PREENCODE.

lparam1--Undefined.

lparam2--Undefined.

ALG₋₋ POSTENCODE

Video driver 206 sends an ALG₋₋ POSTENCODE message after the encode of each frame to instruct the algorithm DLL to copy the encoded data from VRAM into a VFW host buffer using the *pfVram2Host function. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ POSTENCODE are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ POSTENCODE.

lparam1--Far pointer to POSTENCODE₋₋ PARMS structure.

lparam2--Undefined.

The POSTENCODE₋₋ PARMS structure contains the following parameters:

CODEC₋₋ ARGS FAR *pCA--Pointer to parameters needed by decode microcode.

WORD CodecArgsSize--Size of parameters needed by decode microcode.

VIDEOHDR FAR *pVidHdr--Pointer to a Windows VIDEOHDR structure.

ALG₋₋ GET₋₋ PIXELS₋₋ PER₋₋ SECOND

Video driver 206 sends an ALG₋₋ GET₋₋ PIXELS₋₋ PER₋₋ SECOND message when it wants to know how fast the video algorithm microcode 630 can compress an image. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ GET₋₋ PIXELS₋₋ PER₋₋ SECOND are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ GET₋₋ PIXELS₋₋ PER₋₋ SECOND.

lparam1--Undefined.

lparam2--Undefined.

ALG₋₋ SET₋₋ QUALITY

Video driver 206 sends an ALG₋₋ SET₋₋ QUALITY message when it wants to adjust the quality of the compression/decompression algorithm. The values of the alg₋₋ proc0 parameters associated with ALG₋₋ SET₋₋ QUALITY are:

dwAlgInstId--The algorithm instance identifier.

uiAlgMsg--ALG₋₋ SET₋₋ QUALITY.

lparam1--Quality (0-100).

lparam2--Undefined.

Memory Space Management

Memory manager 606 manages the allocation of memory within VRAM 120. During decompression and display processing, video driver 206 uses VRAM 120 to store the compressed bitstreams received from Microsoft® Video for Windows, the decompressed bitmaps generated by programmable processor 118, and the scaled bitmaps generated by display hardware module 122. During capture and compression processing, video driver 206 uses VRAM 120 to store the raw "full frame" uncompressed capture bitmaps generated by capture hardware module 116 and the compressed bitstreams and companded bitmaps generated by programmable processor 118. Memory manager 606 orchestrates the allocation and freeing of linear memory space in VRAM 120 to store efficiently the two-dimensional bitmaps and linear bitstreams used and generated during the video data processing.

Implementation of Copy/Scale Function

Copy/scale manager 616 manages the copy/scale function in which unsealed bitmaps are scaled for display on monitor 108 as video images with dimensions (i.e., height and width) different from those of the unscaled bitmaps. The unscaled bitmaps used to generate the scaled bitmaps may be the decompressed bitmaps generated by programmable processor 118 during decompression and display processing. They may also be either the raw "full frame" uncompressed bitmaps generated by capture hardware module 116 or the companded bitmaps generated by programmable processor 118 during capture and compression processing with monitoring activated.

Implementation of Full-Screen Display Option

Referring now to FIG. 7, there is shown a process flow diagram of the processing managed by view manager 608 to display full-screen video images, according to a preferred embodiment of the present invention. View manager 608 provides the ability to display unscaled bitmaps as full-screen video images without performing the copy/scale function.

After the dimensions of the unscaled bitmaps are specified (block 702 of FIG. 7) and the full-screen display option is selected (block 704), unscaled bitmaps of the specified dimensions are generated (block 706) and converted to analog signals for display with the resolution of the display selected automatically by view manager 608 based on the dimensions of the unscaled bitmap and the dimensions of the display raster (block 708). The resulting analog signals are displayed on monitor 108 (block 710) as full-screen images. The unscaled bitmaps generated at block 706 may be either decompressed bitmaps (generated at block 308 of FIG. 3), raw uncompressed bitmaps (generated at block 404 of FIG. 4), or companded bitmaps (generated at block 406 of FIG. 4). In a preferred embodiment, display hardware module 122 is capable of arbitrarily adjusting raster resolution.

Those skilled in the art will understand that view manager 608 provides efficient display of full-screen video images by avoiding the copy/scale function. In a preferred embodiment, when the full-screen display option is selected, the video data are displayed without VGA keying and therefore without any merging of graphics data. View manager 608 supports full-screen video display of unscaled bitmaps of arbitrary dimensions.

Clipping Video Windows

Clipping manager 614 handles the clipping of video data associated with overlapping windows in a windowed environment.

COFF File Parser

Common object file format (COFF) file parser 612 loads and converts an object file (as stored on host memory 110) into a form that programmable processor 118 can

Managing Interrupt Service Routines

The interrupt service routine manager 620 runs when the video hardware generates an interrupt. The interrupt service routine manager 620 then calls the appropriate module in video driver 206.

Capturing Analog Video Signals

Capture manager 618 manages the capture of analog video signals from camera 102 as raw "full frame" uncompressed bitmaps in VRAM 120 by capture hardware module 116.

Managing Plug & Play Capabilities

Plug & play manager 622 provides plug & play capabilities that are designed to make installation of the hardware as simple as possible for the end user. Preferably, a certain amount of hardware and PC configuration happens before the hardware may be used. The plug & play manager 622 follows the guidelines set forth in the following documents: Plug & Play Device Driver Interface Specification for Microsoft® Windows 3.1 and MS-DOS (Jun. 9, 1993 version 1.0a) and Plug & Play ISA Specification by Intel Corporation (copyright 1993--Intel Corporation & Microsoft Corporation, version 1.01 (EEPROM draft), Jun. 18, 1993).

Video driver 206 is designed to be easily reconfigured to support modifications and upgrades to video hardware subsystem 104. Hardware interface 626 (a hardware abstraction layer) and plug & play software 628 contain most of the hardware-specific information for video driver 206. As such, when video hardware subsystem 104 is modified, most of the changes to video driver 206 will be made only to hardware interface 626 and plug & play software 628.

Management of Background and Foreground Commands

When video system 100 displays video data on raster-based VGA monitor 108, the video data is processed and stored to VRAM 120 at various stages in the process. For example, during monitoring of capture and compression processing, raw uncompressed bitmaps, compressed bitstreams, companded bitmaps, and scaled bitmaps are all stored to VRAM 120.

The video data to be displayed on monitor 108 are stored in display bitmaps. During normal processing, the display bitmaps are the scaled bitmaps generated by programmable processor 118 during the copy/scale function. When the full-screen display option is selected, the display bitmaps may be the raw uncompressed bitmaps, the companded bitmaps, or the decompressed bitmaps, depending on the processing and monitoring options selected. In any case, the display bitmaps contain the video data to be converted to analog signals for display on monitor 108.

The current display bitmap is displayed on monitor 108 by reading the video data in a rasterized manner, i.e., one pixel at a time from left to right and one row at a time from top to bottom. When the bottom right corner of the current display bitmap is reached, the process returns to the top left corner to repeat the raster scan for the next display bitmap. The period between the end of the raster display for the current display bitmap and the beginning of the raster display for the next display bitmap is called the vertical blanking interval (VBI).

In a preferred embodiment of the present invention, the video data for each display bitmap are written over the video data for the immediately preceding display bitmap. If new video data are being written at the same time as the display bitmap area is being raster scanned, then the display of a single video image may contain data from two different video frames. To avoid this undesirable result, video system 100 supports the use of two types of commands: background commands and foreground commands.

Background commands do not directly change the display bitmaps, while foreground commands do directly change the display bitmaps. For example, in capture and compression processing with monitoring of companded bitmaps selected, a command to capture new uncompressed bitmaps does not directly change the display bitmaps. Such a command is preferably a background command. On the other hand, a command to copy/scale companded bitmaps for display does directly change the display bitmaps and is preferably a foreground command.

To avoid the problems of displaying display bitmap dam from two different video frames, foreground commands are preferably implemented only during the vertical blanking interval. Background commands, on the other hand, may be implemented at any time. In a preferred embodiment, background commands are contained in a single background command list and foreground commands are contained in a single foreground command list. The single background and foreground command lists contain all of the background and foreground commands, respectively, even when video system 100 displays two or more video streams at the same time.

Referring now to FIG. 8, there is shown a process flow diagram of the processing of run process manager 624 of FIG. 6 (part of video driver 206 running on host processor 110) to coordinate the implementation of commands contained in the background and foreground command lists, according to a preferred embodiment of the present invention. During raster display, the background commands in the background command list are implemented (block 802 of FIG. 8).

At the start of a vertical blanking interval, the implementation of background command list is interrupted (block 804) and the implementation state of any interrupted background command is saved (block 806). The foreground command list is then implemented (block 808). Implementation of the foreground command list is preferably completed during the VBI. After implementation of the foreground command list is complete, the implementation state of the interrupted background command is restored (block 810) and the implementation of the background command list is resumed (block 812).

Management of Microcode Outside Video for Windows Environment

Video processing systems are typically provided with microcode to implement particular video processing algorithms. In a preferred embodiment of the present invention, video driver microcode 634 of FIG. 6 is the video processing microcode provided with video driver 206 and video hardware subsystem 104. Video driver microcode 634 is the part of video driver 206 that runs on programmable processor 118. Video driver microcode 634 implements video processing functions such as copy/scale.

Microcode manager 610 provides the capability of using video driver 206 to program programmable processor 118 of video hardware subsystem 104 to perform data processing other than the video data processing supported by microcode 634 provided with video hardware subsystem 104. Microcode manager 610 allows a user to load and run loadable microcode 632 on programmable processor 118 outside the environment created by a general-purpose video software program such as Microsoft® Video for Windows.

Microcode manager 610 allows two or more concurrent and independent application programs to run different microcode programs on programmable processor 118, where none, one, or more of the microcode programs are related to video processing. Video driver 206 manages the swapping of the microcode programs between programmable processor 118 and VRAM 120.

Microcode manager 610 can be accessed through the loadable microcode interface (LMI). This interface is used to allocate VRAM through memory manager 606, get view information through view manager 608, and load microcode through microcode manager 610. The LMI interface is defined as follows:

    ______________________________________                                         OpenDriver (LPCSTR Driver, LPCSTR Section, LPARAM 1Param2)                     Driver                                                                         name of the driver to load                                                     Section                                                                        section to find driver in SYSTEM.INI.                                          1Param2                                                                        pointer to LMI.sub.-- OPEN.sub.-- PARMS structure.                             Returns                                                                        handle to driver to use in future calls.                                       Description                                                                              This call will open the driver in such a way as to allow                       access to the Loadable Microcode Interface (LMI)                     CloseDriver (HDRVR Driver, LPARAM 1Param1, LPARAM 1Param2)                     Driver                                                                         Handle of driver to close, previously returned                                           from a call to OpenDriver( )                                         Description                                                                              This call closes the driver, no further access                                 is permitted using driver.                                           SendDriverMessage (HDRVR DRV, UINT msg.                                        DWORD 1Parm1, DWORD 1Parm2)                                                    Drv                                                                            Handle to previously opened driver.                                            msg                                                                            One of the following messages for an LMI driver.                               LMI.sub.-- INIT                                                                LMI.sub.-- TERM                                                                LMI.sub.-- ALLOC.sub.-- VMEM                                                   LMI.sub.-- FREE.sub.-- VMEM                                                    LMI.sub.-- VMEM.sub.-- TO.sub.-- HOST                                          LMI.sub.-- HOST.sub.-- TO.sub.-- VMEM                                          LMI.sub.-- GET.sub.-- VMEM.sub.-- DWORD                                        LMI.sub.-- PUT.sub.-- VMEM.sub.-- DWORD                                        LMI.sub.-- GET.sub.-- VMEM.sub.-- WORD                                         LMI.sub.-- PUT.sub.-- VMEM.sub.-- WORD                                         LMI.sub.-- LOAD.sub.-- MCODE                                                   LMI.sub.-- UNLOAD.sub.-- MCODE                                                 LMI.sub.-- RUN.sub.-- PROCESS                                                  LMI.sub.-- GET.sub.-- VIEW.sub.-- INFO                                         1Parm1                                                                         Defined below, different for each message.                                     1Parm2                                                                         Defined below, different for each message.                                     Description                                                                              This call sends a message to a previously opened driver.                       The messages for an LMI driver are as follows.                       LMI.sub.-- INIT - Initializes usage to the driver.                             Parm1 ----- void                                                               Parm2 ----- void                                                               Return -----0 if ok                                                            LMI.sub.-- TERM - Terminates usage to the driver.                              Parm1 ----- void                                                               Parm2 ----- void                                                               Return -----0 if ok                                                            LMI.sub.-- ALLOC.sub.-- VMEM - Allocates video memory.                         Parm1 ------ DWORD, Size to allocate                                           Parm2 ------ DWORD, Alignment (4=DWORD)                                        Return ------ DWORD, VRAM address, -1 bad                                      LMI.sub.-- FREE.sub.-- VMEM - Frees allocated video memory.                    Parm1 ------ DWORD, VRAM address                                               Parm2 ------ void                                                              Return ------ 0 if ok                                                          LMI.sub.-- VMEM.sub.-- TO.sub.-- HOST - Copies VRAM to host memory.            Parm1 ------ pointer to TRANSBLOCK                                             Parm2 ------ void                                                              Return ------ 0 if ok                                                          TRANSBLOCK {                                                                           WORD pointer Host- Host buffer                                                 DWORD HostOffset - Offset buffer                                               DWORD VAddr - VRAM source address                                              DWORD Size - Number of bytes to copy                                   LMI.sub.-- HOST.sub.-- TO.sub.-- VMEM - Copies host memory to VRAM.            Parm1 ------ Pointer to TRANSBLOCK                                             Parm 2 ------ void                                                             Return ------ 0 if ok                                                          TRANSBLOCK {                                                                           WORD pointer Host - Host source buffer                                         DWORD HostOffset - Offset into buffer                                          DWORD VAddr - VRAM address                                                     DWORD Size - Number of bytes to copy                                   }                                                                              LMI.sub.-- GET.sub.-- VMEM.sub.-- DWORD - Gets a VRAM DWORD.                   Parm1 - DWORD, video memory address                                            Parm2 - void                                                                   Return - DWORD, value at video memory address                                  LMI.sub.-- PUT.sub.-- VMEM.sub.-- DWORD - Puts a DWORD into VRAM.              Parm1 - DWORD address to put DWORD                                             Parm2 - DWORD value to place in VRAM.                                          Return - 0 if ok                                                               LMI.sub.-- GET.sub.-- VMEM.sub.-- WORD - Gets a VRAM WORD.                     Parm1 - DWORD, video memory address                                            Parm2 - void                                                                   Return - WORD, value at VRAM address                                           LMI.sub.-- PUT.sub.-- VMEM.sub.-- WORD - Puts a WORD into VRAM.                Parm1 - DWORD address to put WORD                                              Parm2 - WORD value to place in VRAM                                            Return - 0 if ok                                                               LMI.sub.-- GET.sub.-- VIEW.sub.-- INFO - Gets view information.                Parm1 - void                                                                   Parm2 - void                                                                   Return - VIEWINFO pointer, view descriptor                                     VIEWINFO{                                                                              DWORD YAddr, VAddr, UAddr                                                      WORD YPitch, VPitch, UPitch                                                    WORD XSubsample, YSubsample                                                    WORD xpixels. ypixels                                                  }                                                                              LMI.sub.-- LOAD.sub.-- MCODE - Loads microcode into VRAM.                      Parm1 - LPSTR, name of microcode to load                                       Parm2 - HMODULE, module containing microcode                                   Return - DWORD VRAM address of microcode,                                      -1 if load failed                                                              Note: Microcode must be a resource in the                                      module referenced by Parm2                                                     LMI.sub.-- UNLOAD.sub.-- MCODE - Unloads microcode from VRAM.                  Parm1 - DWORD, VRAM address of microcode                                       Parm2 - void                                                                   Return - 0 if ok                                                               LMI.sub.-- RUN.sub.-- PROCESS - Runs microcode loaded in VRAM.                 Parm1 - PROCBLOCK pointer, process block                                       Parm2 - void                                                                   Return - 0 if ok                                                               PROCBLOCK {                                                                     LMI.sub.-- CMD.sub.-- BLOCK pointer {                                           DWORD Addr - Address of microcode                                              WORD nBytes - bytes following                                                 }                                                                                    int ExecutionPriority - either background or foreground                        int (pointer NotifyFunction)(                                                     DWORD User1                                                                    DWORD User2                                                                    LMI.sub.-- CMD.sub.-- BLOCK pointer pCmd                                      );                                                                              DWORD User1 - passed to callback                                               DWORD User2 - passed to callback                                               int NotifyPriority - High or Low                                               DWORD ProcessID - Returned process id                                        }                                                                      ______________________________________                                    

It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the principle and scope of the invention as expressed in the following claims. 

What is claimed is:
 1. A computer-implemented process for raster displaying two or more streams of video data on a monitor of a computer system, comprising the steps of:(a) processing the two or more streams of video data by implementing a single background command list comprising one or more programmable background commands for each stream of video data using a single processor; (b) processing the two or more streams of video data by implementing a single foreground command list comprising one or more programmable foreground commands for each stream of video data using the single processor, where the single processor implements the foreground command list only during a vertical blanking interval of the display raster of the monitor; and (c) displaying the processed two or more streams of video data simultaneously in two or more windows on the monitor.
 2. The process of claim 1, wherein step (b) comprises the steps of:(1) interrupting the implementation of a background command at the start of the vertical blanking interval; (2) saving the state of implementation of the interrupted background command; (3) implementing the foreground command list; (4) restoring the state of implementation of the interrupted background command at the termination of the foreground command list; and (5) resuming implementation of the background command.
 3. The process of claim 1, wherein:step (a) comprises the step of processing the video data without altering a display bitmap, wherein the display bitmap is displayed during the current display raster; and step (b) comprises the step of processing the video data to alter the display bitmap, wherein the altered display bitmap is displayed during the next display raster.
 4. A computer system for raster displaying two or more streams of video data, comprising:(a) a single processor for processing the two or more streams of video data: by implementing, using the single processor, a single background command list comprising one or more programmable background commands for each stream of video data; and by implementing, using the single processor, a single foreground command list comprising one or more programmable foreground commands for each stream of video data; and (b) a monitor for displaying the processed two or more streams of video data simultaneously in two or more windows on the monitor, wherein the single processor implements the foreground command list only during a vertical blanking interval of the display raster of the monitor.
 5. The system of claim 4, wherein the processing means comprises:(1) means for interrupting the implementation of a background command at the start of the vertical blanking interval; (2) means for saving the state of implementation of the background command; (3) means for implementing the foreground command list; (4) means for restoring the state of implementation of the background command at the termination of the foreground command list; and (5) means for resuming implementation of the background command.
 6. The system of claim 4, wherein the processing means comprises:(1) means for processing the video data by implementing the background command list without altering a display bitmap, wherein the display bitmap is displayed during the current display raster; and (2) means for processing the video data by implementing the foreground command list to alter the display bitmap, wherein the altered display bitmap is displayed during the next display raster.
 7. A computer-implemented process for raster displaying two or more streams of video data on a monitor of a computer system, comprising the steps of:(a) raster displaying a display bitmap thereby displaying the two or more streams of video data simultaneously in two or more windows on the monitor; (b) processing the two or more streams of video data by implementing, using a single processor, a single background command list comprising one or more programmable background commands for each stream of video data during the raster display of the display bitmap, wherein the implementation of the background command list does not alter the display bitmap; (c) processing the two or more streams of video data, using the single processor, by implementing a single foreground command list comprising one or more programmable foreground commands for each stream of video data, wherein the single processor implements the foreground command list during a vertical blanking interval of the display raster of the monitor, wherein the implementation of the foreground command list alters the display bitmap; and (d) raster displaying the altered display bitmap after the vertical blanking interval thereby displaying the processed two or more streams of video data simultaneously in the two or more windows on the monitor.
 8. The process of claim 7, wherein step (c) comprises the steps of:(1) interrupting the implementation of a background command at the start of the vertical blanking interval; (2) saving the state of implementation of the background command; (3) implementing the foreground command list; (4) restoring the state of implementation of the background command at the termination of the foreground command list; and (5) resuming implementation of the background command.
 9. A computer system for raster displaying two or more streams of video data, comprising:(a) a single processor for processing the two or more streams of video data to generate a display bitmap for display; and (b) a monitor for displaying the display bitmap, thereby displaying the two or more streams of video data simultaneously in two or more windows on the monitor, wherein:the single processor generates the display bitmap corresponding to the two or more streams of video data; the monitor raster displays the display bitmap in the two or more windows on the monitor; the single processor processes the two or more streams of video data by implementing a single background command list comprising one or more programmable background commands for each stream of video data during the raster display of the display bitmap, wherein the implementation of the background command does not alter the display bitmap; the single processor processes the two or more streams of video data by implementing a single foreground command list comprising one or more programmable foreground commands for each stream of video data only during a vertical blanking interval of the display raster of the monitor, wherein the implementation of the foreground command list alters the display bitmap; and the monitor raster displays the altered display bitmap after the vertical blanking interval thereby displaying the processed two or more streams of video data simultaneously in the two or more windows on the monitor.
 10. The system of claim 9, wherein the processing means comprises:(1) means for interrupting the implementation of a background command at the start of the vertical blanking interval; (2) means for saving the state of implementation of the background command; (3) means for implementing the foreground command list; (4) means for restoring the state of implementation of the background command at the termination of the foreground command list; and (5) means for resuming implementation of the background command. 